The practically viable methods of comminution differ by is the type of stress or deformation of the particles to be comminuted in the crushing chamber. When stressing the particles between two roller surfaces, pressure, shear and tensile stresses are generated in the particles. The design of the roller surface as well as the rate of rotation determine the type of stress and the intensity.
U.S. Pat. No. 3,240,436 describes a crushing apparatus for solid materials. In this case glass products, such as television tubes or the like are regarded as solid materials.
The counter-rotating crushing rollers are driven synchronously by way of a joint drive mechanism and comprise crushing teeth in the form of annular gears and arranged in the peripheral and longitudinal axial directions. The cross-section through each crushing roller shows a plurality of crushing teeth per annular gear so that in the region where the individual crushing teeth of the two crushing rollers comb with one another relatively small crushing chambers are formed in the entry region above the crushing rollers. It is shown that even relatively large glass products may be gripped by the teeth and are pre-crushed in the course of a first crushing process. As the crushing gap of the counter-rotating crushing rollers further decreases, a second, subsequent comminution is performed.
EP-B 0 167 178 describes a mineral crusher comprising two crushing rollers, each of them equipped with a number of mineral crusher teeth projecting radially from the roller, the teeth on each roller being arranged in groups, extending in peripheral direction, spaced axially along the roller, the groups of teeth extending in peripheral direction being so arranged on a roller that they are positioned between adjoining groups of teeth of the other roller, extending in the peripheral direction and being axially spaced apart from them, so that in the event of counter-rotation of the rollers the teeth of the individual groups pass between two axially spaced teeth in adjoining groups of teeth on the other roller, seizing in the course thereof mineral lumps between one another, effecting the breaking up or crushing of the said lumps. The teeth of each roller are so arranged in relation to one another and are of such size and shape that they define a number of discrete, peripherally spaced, spiral or helical configurations extending along the roller. Each roller includes therefore tooth formations extending spirally from one end to the other, in which context the helix may run in the same or in the opposite direction. The object and purpose of the spiral or helical configuration of the crushing teeth is based on transporting the material to be comminuted in the longitudinal direction of the crushing rollers and in comminuting the former during transport. However, an arrangement of the spiral or helical tooth formation in the same direction would in this case be non-sensical, as no defined transport can be performed. This is only possible when the helices are arranged counter-directionally.
A mineral crusher designed in this manner comprises relatively few teeth per annular gear, viewed in the peripheral direction, so that with counter-rotating rollers a larger crushing chamber is formed already, serving to comminute larger lumps as well. However, it is a drawback of this mineral crusher that the material to be crushed must be fed essentially from the end face side in order to exploit the transport effect, thereby causing various conditions of wear—even when considering the transport of the material in the longitudinal direction of the rollers.
If the material were to be fed elsewhere than at the end, transport would take place, but it would not be optimal and it would be undefined.
The present invention is based upon the state of the art as established by EP 0 167 178, i.e. by a slow running double roller crusher. Such machines are used both for the comminution of medium-hard rock as well as for materials with a tendency to cake, i.e. brown and hard coal, limestone, clay marl and similar raw materials. Parallel and counter-rotating crusher rollers are equipped—as set out in the characterising part of the first patent claim—with crushing teeth, the size, shape and configuration of which define, during the interaction of both rollers, a crushing chamber, ensuring the required quality of the discharge particle size and the throughput performance during comminution.